1. Technical field
The present invention relates to methods and systems for determining the positions of access points and end-user devices of a wireless radio system. More particularly the present invention relates to methods and systems for determining the positions of access points and end-user devices of WiFi systems, i.e. systems working according to the IEEE 802.11 standard.
2. Description of related art
The availability of Wifi systems has grown considerably over the recent years. Some companies offer tools for performing a worldwide hotspot (access point) search. Based on a street address provided by the user, the tools retrieve from a database of hotspots the nearest hotspot(s) for the user. This database of hotspots is called a radio-map. The user is provided with the name and location of the hotspots, as well as the access type (commercial, free of charge). Radio-maps may be used either online (with an available Internet connection) or offline (without an available Internet connection) by end-user devices equipped with Wifi functionality.
Every day, many new hotspots become available. For this reason, the radio-map should be updated and expanded, regularly. This can be done manually, for example by users, by assigning to each hotspot its position or automatically, by a method known as radio-map war-driving. This latter method consists in driving around in an area to be covered, receiving WiFi signal patterns containing information of the hotspots detected and associating the WiFi signal patterns to the position where they were measured. Typically, the way to determine the measurement position is by using a GPS receiver. When a single hotspot is contained in WiFi signal patterns (also called “fingerprints”) taken in different, known positions, enough information is available to calculate the position of such a hotspot.
Radio-map war-driving has some serious drawbacks. First of all, it is not possible to access all places with a motor vehicle, so some hotspots may not be detected by war-driving. Furthermore, war-driving is expensive.
The radio-map is used by WiFi positioning services. Such services use the wireless signals emitted by the access points and the position of the access points in the radio-map to determine the current position of the WiFi enabled (end-user) device. Wifi based positioning of end-users has been described widely in research papers and is being used by companies within different areas such as logistics, health care, visitor guidance, etc. However, frequently the positioning results are not so accurate.
This limited accuracy is caused amongst others by the following error sources:                The signal power emitted by a hotspot is unknown and may be different for each hardware type. The hotspot does not send any information on the emitted signal power on its broadcasting message and therefore, if the received power signal is low, it is not possible to know if is due to a low signal power emitted or just due to a long distance between the measuring device and the hotspot.        Wifi signals go through walls, roofs, etc. and therefore, again, if a low power signal is received, it is not possible to know if this is due to a low emission power or due to a lot of walls between the hotspot and the receptor.        The sensitivity of Wifi enabled devices is very different from one another. Two different devices (a phone and a PDA, for instance) at the same place could very well measure different power signals in spite of being located at the same scenario.        Each device manufacturer may have his own device software driver implementation, so that the received power signal is interpreted in different ways from one device driver to another in spite of being located at the same scenario.        The power of the signals of some of the access points that are used for the positioning is low.        The position of some of the access points that are used for the positioning algorithm is not very accurate.        
It is a first object of the invention to provide a method and a system enabling the update and expansion of a radio-map in a cost efficient way.
It is a second object of the invention to provide positioning services with an improved quality and accuracy compared to known techniques.